1. Field of the Invention
The present invention relates to an engine having a cartridge type transmission and to a cartridge drum transmission that is freely detachable and attachable from/to the engine.
2. Description of Background Art
There is a type of engine, serving as an internal combustion engine for a motorcycle and the like, which has a transmission for rotating a shift drum by a driver's manipulation to shift gears. See, for example, Examined Japanese Patent Publication No. 2-29906, Page 5, FIG. 4. The transmission described in Examined Japanese Patent Publication No. 2-29906 includes a main shaft, a counter shaft, a shift fork shaft, and a shift drum, which are pivotally supported in a crankcase which is divided into two parts on the left and right sides. The shift drum is arranged forward of the main shaft and on the downside thereof. The counter shaft is arranged backward of the main shaft and on the downside thereof. The shift fork shaft is arranged on the downside of the main shaft, and a shift fork for the main shaft and a shift fork for the counter shaft are inserted into one shift fork. Furthermore, a change spindle serving as an oscillation center for the shift arm which rotates the shift drum is arranged below the shift drum.
There is also a type of engine, serving as an internal combustion engine for a motorcycle and the like, which has a shift drum transmission for rotating a shift drum by a driver's manipulation to shift gears. See, for example, Japanese Utility Model Laid-Open Application Publication No. 63-22358, Pages 2 and 3, and FIGS. 1 and 2.
As for this type of shift drum transmission, a cam plate is fixed on one end of the shift drum for shifting gears. The cam plate has a shape of a star, on the periphery of which grooves that are respectively associated with the transmission gears are provided. In addition, on the cam plate, drum pins are disposed facing to the shift drum side. A hook piece of a shift arm which rotates the shift drum is engaged with the drum pins and a stopper roller, which stops the rotation of the shift drum, elastically contacts the grooves of the cam plate.
The shift arm is arranged at a more internal side than the cam plate, and is coupled with a change pedal which a driver operates with his/her foot. When the driver operates the change pedal, the shift arm is rotated, so as to allow the cam plate and the shift drum, which are engaged via the drum pins, to start rotating. At this timing, when the stopper roller is disengaged from a groove, causing the shift drum to rotate, and then, the stopper roller becomes engaged with the next groove, the rotation of the shift drum is stopped. As a result, the transmission gear of the shift drum type transmission is changed.